Electroplated tin and tin/lead alloy solder coatings are used extensively in the electronics industry in the manufacture of printed wiring boards (PWB), electrical contacts and connectors, semiconductor packaging, electrical conduits, and other related parts. These plated solder coatings must be pore free or corrosion resistant, display long tern solderability and be free from solderability failures such as non-wetting and dewetting.
Tin and tin/lead alloy solder coatings are typically deposited using high speed electroplating equipment in order to maximize productivity and hence, profitability. High speed electroplating is achieved with high current densities that tend to incorporate significant quantities of organics into the plated solder coatings. When these organic quantities become too large, solderability failures can occur.
Bright plated solder coatings produced in high speed electroplating processes using conventional electroplating solutions usually have undesirably large quantities of organics incorporated into them. This is because conventional electroplating solutions typically include many organic additives or agents which brighten the plated surfaces. These brightening agents produce electro-chemical and chemical by-products which are incorporated in the deposit during electroplating, thus increasing the organic content of the solder coating. During high speed electroplating, these by-products accumulate in the electroplating solution at a fast rate. The accumulation of these by-products in the electroplating solution increases the organic content of the solder coatings, thus leading to an unacceptable number of solderability failures. Therefore, in PWB and semiconductor packaging applications, such as leadframes, where solderability and productivity are very critical, plated solder coatings having matte or satin bright finishes are utilized because they can be produced in high speed electroplating processes with tolerable quantities of organics.
This is unfortunate because bright plated solder coatings have some distinct advantages over plated solder coatings with matte and satin bright finishes in certain areas other than solderability. On-line automatic inspection is easily implemented when bright plated solder coatings are used. Bright plated solder coatings are also less likely to have plating stains and are cosmetically superior.
Bright plated solder coatings with satisfactory solderability can only be achieved at low current densities with conventional electroplating solutions. The use of low current densities reduces the plating speed of the electroplating process. This in turn, significantly reduces productivity and thus, the profitability of the parts.
Accordingly, there is a need for an electroplating solution that produces bright plated solder coatings with low organic content at the high current densities employed in high speed electroplating processes.